[v2,4/7] HID: i2c-hid: elan: fix reset suspend current leakage

The Elan eKTH5015M touch controller found on the Lenovo ThinkPad X13s
shares the VCC33 supply with other peripherals that may remain powered
during suspend (e.g. when enabled as wakeup sources).

The reset line is also wired so that it can be left deasserted when the
supply is off.

This is important as it avoids holding the controller in reset for
extended periods of time when it remains powered, which can lead to
increased power consumption, and also avoids leaking current through the
X13s reset circuitry during suspend (and after driver unbind).

Use the new 'no-reset-on-power-off' devicetree property to determine
when reset needs to be asserted on power down.

Notably this also avoids wasting power on machine variants without a
touchscreen for which the driver would otherwise exit probe with reset
asserted.

Fixes: bd3cba00dcc6 ("HID: i2c-hid: elan: Add support for Elan eKTH6915 i2c-hid touchscreens")
Cc: stable@vger.kernel.org	# 6.0
Cc: Douglas Anderson <dianders@chromium.org>
Tested-by: Steev Klimaszewski <steev@kali.org>
Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
---
 drivers/hid/i2c-hid/i2c-hid-of-elan.c | 59 +++++++++++++++++++++------
 1 file changed, 47 insertions(+), 12 deletions(-)

Hi,

On Tue, May 7, 2024 at 7:48 AM Johan Hovold <johan+linaro@kernel.org> wrote:
>
> @@ -40,17 +41,17 @@ static int elan_i2c_hid_power_up(struct i2chid_ops *ops)
>                 container_of(ops, struct i2c_hid_of_elan, ops);
>         int ret;
>
> +       gpiod_set_value_cansleep(ihid_elan->reset_gpio, 1);

Could probably use a comment above it saying that this is important
when we have "no_reset_on_power_off" and doesn't do anything bad when
we don't so we can just do it unconditionally.


> +
>         if (ihid_elan->vcc33) {
>                 ret = regulator_enable(ihid_elan->vcc33);
>                 if (ret)
> -                       return ret;
> +                       goto err_deassert_reset;
>         }
>
>         ret = regulator_enable(ihid_elan->vccio);
> -       if (ret) {
> -               regulator_disable(ihid_elan->vcc33);
> -               return ret;
> -       }
> +       if (ret)
> +               goto err_disable_vcc33;
>
>         if (ihid_elan->chip_data->post_power_delay_ms)
>                 msleep(ihid_elan->chip_data->post_power_delay_ms);
> @@ -60,6 +61,15 @@ static int elan_i2c_hid_power_up(struct i2chid_ops *ops)
>                 msleep(ihid_elan->chip_data->post_gpio_reset_on_delay_ms);
>
>         return 0;
> +
> +err_disable_vcc33:
> +       if (ihid_elan->vcc33)
> +               regulator_disable(ihid_elan->vcc33);
> +err_deassert_reset:
> +       if (ihid_elan->no_reset_on_power_off)
> +               gpiod_set_value_cansleep(ihid_elan->reset_gpio, 0);

Small nit about the error label: it sounds as if when you go here you
_will_ deassert reset when in actuality you might or might not
(depending on no_reset_on_power_off). Personally I prefer to label
error jumps based on things I've done instead of things that the error
jump needs to do, so you could call them "err_enabled_vcc33" and
"err_asserted_reset"...

I don't feel that strongly about it, though, so if you love the label
you have then no need to change it.


> @@ -67,7 +77,14 @@ static void elan_i2c_hid_power_down(struct i2chid_ops *ops)
>         struct i2c_hid_of_elan *ihid_elan =
>                 container_of(ops, struct i2c_hid_of_elan, ops);
>
> -       gpiod_set_value_cansleep(ihid_elan->reset_gpio, 1);
> +       /*
> +        * Do not assert reset when the hardware allows for it to remain
> +        * deasserted regardless of the state of the (shared) power supply to
> +        * avoid wasting power when the supply is left on.
> +        */
> +       if (!ihid_elan->no_reset_on_power_off)
> +               gpiod_set_value_cansleep(ihid_elan->reset_gpio, 1);
> +
>         if (ihid_elan->chip_data->post_gpio_reset_off_delay_ms)
>                 msleep(ihid_elan->chip_data->post_gpio_reset_off_delay_ms);

Shouldn't  the above two lines be inside the "if
(!ihid_elan->no_reset_on_power_off)" test? If you're not setting the
reset GPIO then you don't need to do the delay, right?


> @@ -79,6 +96,7 @@ static void elan_i2c_hid_power_down(struct i2chid_ops *ops)
>  static int i2c_hid_of_elan_probe(struct i2c_client *client)
>  {
>         struct i2c_hid_of_elan *ihid_elan;
> +       int ret;
>
>         ihid_elan = devm_kzalloc(&client->dev, sizeof(*ihid_elan), GFP_KERNEL);
>         if (!ihid_elan)
> @@ -93,21 +111,38 @@ static int i2c_hid_of_elan_probe(struct i2c_client *client)
>         if (IS_ERR(ihid_elan->reset_gpio))
>                 return PTR_ERR(ihid_elan->reset_gpio);
>
> +       ihid_elan->no_reset_on_power_off = of_property_read_bool(client->dev.of_node,
> +                                               "no-reset-on-power-off");

Personally, I'd rather you query for the property before you request
the GPIO and then request the GPIO in the "powered off" state just to
keep everything in the most consistent state possible.


-Doug